JPS5863864A - Curpent/voltage converting circuit - Google Patents

Abstract

PURPOSE:To attain current/voltage conversion almost without errors in case of the current measurement of the primary conductor in a wide range by changing load resistance in accordance with the size of the primary current value. CONSTITUTION:One of the secondary winding of a current transformer 2 is connected to a zero potential line and the other to a common terminal K1 of an alteration switch 5a. The switching terminal L1 of the switch 5a is inputted to the negative input terminal of an amplifier 6a and terminals M1, N1 are inputted to the positive input terminal of an amplifier 6. A common terminal K2 and a terminal L2 of an alteration switch 5b are connected to the positive input terminal of the amplifier 6 and the output terminal of the amplifier 6a respectively and terminals M2, N2 are connected to a zero potential line through load resistors 4b, 4c respectively. The negative input terminal of the amplifier 6 is connected to the zero potential line through a resistor 7 and to its output terminal through a resistor 8 respectively and the negative input terminal of the amplifier 6a is connected to its output terminal through a resistor 9 and the positive input terminal is directly connected to the zero potential line respectively. The load resistors 4b, 4c are selected in accordance with the current value of the primary conductor 1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for inputting a detected current from a secondary winding of a current transformer, particularly a flange large current transformer, and converting it into a voltage.

To monitor the operating status of electrical equipment and manage loads,
It is necessary to use a device that measures power consumption, power factor, etc. from the input current and voltage of the equipment.

In this case, it is desirable to measure the power of the equipment while it is in use without cutting the electrical wiring of the equipment. Therefore, a clamp-type current transformer is being supplied in which the ring-shaped core of the current transformer can be opened and closed using a flange type, and the electrical wiring is interposed within the ring-shaped core, and then the ring is closed to measure the input current of the equipment. ing.

The detected current from the secondary 1111 winding of the clamp type current transformer is basically amplified and converted to a voltage by the circuit shown in FIG.

In Figure 1, 1 is the primary conductor of the clamp type current transformer which is the input current line of the equipment, 2 is the clamp type current transformer, 3 is the connector that connects the clamp type current transformer to the main body of the device, and 4 is the load Resistor, 6 is amplifier (vDD is positive power supply, V is negative power supply)
, 7 and 8 are amplification resistors, and 10 is a detection output.

The current flowing through the primary conductor l is the current flowing through the clamp type current transformer 2.
A current inversely proportional to the number of secondary windings is detected from the clamp type current transformer 2 by the secondary winding. This detection current flows to the load resistor 4 via the connection connector 3, and the voltage generated across the load resistor 40 is amplified by the amplifier 6 and resistors 7 and 8 and output as a detection output 10.

However, in the circuit of Fig. 1, since the load resistance 4 is constant,
- If the range of current values flowing through the next conductor 1 is wide, the range of small current values cannot be measured.

For example, the negative side current value range, that is, the measurement range is up to 500.
A, minimum 0.25 A, negative side current value 500 A
If the output 10 of the amplifier 6 is IOV, the output of the amplifier 6 will be 0.005 V when the negative side current value is 0.25 A, and an accurate output cannot be obtained due to the characteristics of the amplifier 6 such as the offset voltage.

Generally, the negative side current measurement range is wide, for example 0.2
From 5A to 600A, etc., a range switching method such as the example shown in FIG. 2 is actually used.

In FIG. 2, instead of the load resistor 40 in FIG.
a s 4b * 4C1kM&ge, its load resistance 4a
.

4b and 4c are switched by a changeover switch 5. The same reference numerals in the drawings indicate the same or corresponding parts.

In Figure 2, the negative side current measurement range is divided into three types of ratings (
For example, 5A, 50A, 500A, etc.), switch the changeover switch 5 for each rating, and load resistance 4.
By a, 4b, 4c, amplified heat: A6 output'
The voltage 10 is output as a constant voltage for each rating.

Here, if the load resistance is, for example, 10Ω when the -order 11III current measurement rating is 500A, then when the rating is 5A, the load resistance is 10Ω.
It becomes o times IKΩ.

However, in the current transformer 2, the error increases as the negative Jul increases. Therefore, the circuit shown in FIG. 2 has the disadvantage that the error becomes large when the primary supply current, at which the load resistance is switched to the largest value, is small.

Recently, from the point of view of energy saving? High-level monitoring and load management are desired, and it is desirable that devices that use clamp-type current transformers as inputs be able to measure with greater accuracy over a wide measurement range.

The present invention has been made in view of the above-mentioned circumstances, and has means for converting current into voltage using an ideal circuit in which the load resistance is almost zero when the negative side current is small. - It is an object of the present invention to provide a device for converting a secondary current from a clamp-type current transformer into a voltage with little error over a wide measuring range of secondary current.

FIG. 3 is a block diagram of one embodiment of the present invention.

5a and 5b are changeover switches that switch in conjunction; 6
a is an amplifier, and 9 is an amplification resistor.

- The secondary conductor l passes through the iron core of the clamp type current transformer 2, one of the secondary windings of the current transformer 2 is connected to the zero potential line of the internal circuit, and the other is connected to the common of the changeover switch 5a. It is connected to terminal Kl. Among the switching terminals of the selector switch 5a, the Ll terminal is input to the negative input terminal of the amplifier 6a, and the Ml and Nl terminals are input to the positive input terminal of the amplifier 6. In addition, 2 is connected to the common terminal of the changeover switch 5b.
The L2 terminal is connected to the output terminal of the amplifier 6a, and the L2 terminal is connected to the output terminal of the amplifier 6a. N2 is each load resistance 4
It is connected to the zero potential line of the internal circuit via terminals b and 4c. The negative input terminal of the amplifier 6 is connected to the zero potential line via a resistor 7 and to the output terminal via a resistor 8, and the negative terminal of the amplifier 6a is connected to the output terminal via a resistor 9. The positive input terminal is followed by a zero potential line.

In FIG. 3, for example, the current measurement range of the negative side conductor 1 is 0.25A to 600A, and the current measurement range is 5A.

When measuring by switching between 50A and 500A, set the switching terminals of changeover switches 5a and 5b to L when the rated value is 5A.
L, L2 terminal is rated! When the rating is 5OA, the Ml and N2 terminals are connected to the common terminal Kl, and when the rating is 500A, the Nl and N2 terminals are connected to the common terminal Kl.

Here, when the negative side conductor l has a rating of 5 A, the detected current of the clamp type current transformer 2 is amplified by the amplifier +l@446a, and then further amplified by the amplifier 6 and output.

At this time, since the input impedance of the amplifier 6a is y zero, the load resistance seen from the clamp type current transformer 2 is g zero, and the current can be ideally converted into a chemical pressure.

Further, in the case of rated voltages of 50A and 500A, the voltages are converted into voltages by load resistors 4b and 4c, respectively, and amplified by an amplifier 6 and output. In this case, the load resistor 4b.

4C is a small impedance. For example, if the load resistance 4C when the rating is 500A is 10Ω, the load resistance 4b when the rating is 50A is 100Ω, and the clamp type current transformer 2
The load is light (characteristics with few errors can be obtained).

Therefore, even if the current in the negative side conductor 1 is large, the third
It is conceivable that the amplifier 6a in the figure receives all the current, but since the output current of a typical amplifier is about 5 mA at most, for example, 500 A flows through the negative side conductor l, and the number of secondary windings of the clamp type current transformer 2. When 2000T, the secondary current of the clamp type current transformer 2 flows as M250mA, which cannot be handled by the output of the amplifier 6a. There is also the idea of connecting a current booster after the amplifier, but the current booster also has its limits and cannot be said to be sufficient.

FIG. 4 is a block diagram of another embodiment of the invention.

In contrast to Fig. 3 of the rabbit, where the changeover switches 5n and 5b are provided on the amplification 'a6a and 6 sides of the connection connector 3,
In this embodiment, the changeover switches 5a, ! 'ib and load resistors 4b and 4c are provided on the clamp type current transformer 2a side.

FIGS. 5(a) and 5(b) are block diagrams of still another embodiment of the present invention.

Figure 5 (a) * (b) shows that clamp-type current transformers 2, 2b, and 2c are provided for each rating, and when the measurement current is small without using a changeover switch, use the method shown in Figure 5 (a). Connect with connector 3b, and if the measured current is large, connect the fifth
As shown in Figure (b), they are connected by a connector 3C. In addition,
This shows that when the current transformer is 2b or 2C, the load resistance is 4b or 4C.

The changeover switches 5a and 5b in FIG. 3 may be replaced with semiconductor switches such as analog switches.

Further, although the clamp type current transformer 2 has been described, the present invention can be applied to general current transformers.

Thus, according to the present invention, when the measured current of the negative side conductor is small, whereas the load resistance of the conventional clamp type current transformer is large and the error is large, the load resistance is An ideal current-to-voltage conversion circuit can be obtained, which can obtain an output with a small error and has a small error when measuring current in a wide range of -order conductors.

[Brief explanation of drawings]

Figures 1 and 2 are block diagrams of conventional circuits, Figure 3 is a block diagram of one practical example of the present invention, Figure 4 is a wiring diagram of another embodiment of the present invention, and Figure 5 (a). +tb) is a connection diagram of still another embodiment of the present invention. l...-Next conductor, 2, 2a, 2b, 2c
... Clamp type current transformer, 3, 3a, 3b,
3c...Connector for connection, 4, 4a, 4b,
4cm -- Load resistance, 5, 5a, 5b -- Changeover switch, 6, 6a -- Amplifier, 7, 8.9 -- Amplification resistor, ] 0 -- Detection output. (11) Figure 1 v7z mouth

Claims (1)

[Scope of Claims] 1. In a circuit which interposes a conductor of a circuit to be measured as the primary side of a current transformer and extracts the current of the secondary winding of the current transformer and converts it into voltage, one of the A first amplifier has an input terminal connected to zero potential and a feedback resistor connected from its output terminal to the other input terminal; A second amplifier is provided with a feedback resistor connected to the input terminal, one output terminal of the secondary winding is connected to zero potential, and when the current to be detected is small, the output of the other secondary winding is connected to the zero potential. The other input end of the first amplifier is connected to the other input end of the first amplifier, and the output end of this first amplifier is connected to the other input end of the second amplifier, and when the current to be detected is large, the secondary (Ill @ A load resistor corresponding to the range is connected between both ends of the output end of the ν gland, and the other output end of the secondary winding is connected to the other input end of the second amplifier. 2. The current-to-voltage conversion circuit according to claim 1, wherein the range of the current to be detected is switched at a stage before the first and second amplifiers. 3. The current-voltage conversion circuit according to claim 1, wherein the range of the current to be detected is switched at the output end of the secondary winding of the current transformer. 4. The current to be detected. Switching of the range is performed by a terminal of a connector which is provided with the current transformer having a load resistance suitable for the range at its output end and which is provided between the current transformer and the first and second amplifiers. The current-voltage conversion circuit according to claim 1, characterized in that the current-voltage conversion circuit is implemented by connection.